An official website of the United States government
Abstract The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F6TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F6TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm2V−1s1being estimated from SCLC measurements for BTBT:F6TNAP and CBZ:F6TNAP cocrystals.
more »
« less
Donor–Acceptor Interactions of C 60 F 18 with Polycyclic Aromatic Hydrocarbons: Size Effects in Bulk Crystallization and Surface Constraints
An in‐depth study of donor–acceptor (D/A) interactions between the high‐dipole acceptor C60F18(A) and polycyclic aromatic hydrocarbon (PAH) donors—pyrene, perylene, and coronene—reveals a surprisingly strong PAH size influence on the D/A complex stoichiometry and ordering in co‐crystals. The crystallographic study shows the tendency of D/A mixtures to form stacked layered structures for the larger PAHs, perylene and coronene, while the role of aromatic π–π interactions diminishes, in contrast to the smaller pyrene/C60F18system. The behavior of the layered‐D/A assemblies is investigated by utilizing sequential deposition and co‐evaporation of C60F18and coronene on Au(111) surfaces. Scanning tunneling microscopy shows that the flat lying configuration adopted by coronene on the metal, which forms highly ordered close‐packed monolayers stabilized by the interaction between their π electrons and the high density of gold surface states, hinders the formation of the ordered assemblies of the corresponding co‐crystal. The influence of the substrate plus the critical role played by electronic and steric effects in the co‐crystal formation are believed to cause the lack of viability. However, it is remarkable that, on the surface, adsorbed single C60F18molecules are well centered on top of one coronene molecule, facilitating charge transfer between D and A molecules.
more »
« less
- Award ID(s):
- 2153922
- PAR ID:
- 10615004
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPlusChem
- ISSN:
- 2192-6506
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Because traditional paleofire archives (e.g., burn scars on trees, charcoal in lake sediments) are not available in all settings, new ways of reconstructing past fire activity are needed. We focus here on polycyclic aromatic hydrocarbons (PAHs) in stalagmites. PAHs are organic molecules composed of two or more fused aromatic rings formed through incomplete combustion of organic matter, and vary in molecular weight depending on combustion conditions. Because the use of PAHs in stalagmites as a paleofire indicator is still in its infancy and because the production, deposition, and transport of PAHs into a cave is a complex and multi-faceted system, we tested the reproducibility of PAHs in two coeval and precisely-dated aragonite stalagmites – KNI-51-F and KNI-51-G - from KNI-51 (15.3°S, 128.6°E), a shallow cave located in the Kimberley region of tropical Western Australia. KNI-51-F and KNI-51-G span 1110-1620 CE and 1310-1630 CE, respectively. Each was hand-milled for analysis in continuous sections spanning approx. 2 mm-tall intervals at Ca’ Foscari University. Owing to differences in growth rate, temporal resolutions for KNI-51-F and KNI-51-G were 3±2 and 1±0.4 yr/sample, respectively. Chemical preparations and analysis methods follow those of Argiriadis et al. (2019) Analytical Chemistry, volume 91. In order to assess replication between the two stalagmites, we compared total abundances of low molecular weight (LMW: Napthalene, Acenaphthylene, Acenaphthene, Fluorene), medium molecular weight (MMW: Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benzo(a)Anthracene, Chrysene, Retene), and high molecular weight (HHM: Benzo(b)Fluoranthene, Benzo(k)Fluoranthene, Benzo(e)Pyrene, Benzo(a)Pyrene, Perylene, Benzo(ghi)Perylene, Indeno(1,2,3-c,d)Pyrene, Dibenzo(A,H)Anthracene) PAHs. Total abundances of LMW, MMW, and HMW PAHs are similar (<10 ng/g) except for HMW PAHs in KNI-51-G, which are generally <1 ng/g. Total LMW and MMW abundance time series replicate well, with multiple synchronous multidecadal periods characterized by consistently low PAH abundances, suggestive of reduced bushfire activity, punctuated by intervals of high PAH abundances, likely reflecting frequent bushfire. Less coherence exists between HMW PAHs.more » « less
-
Electron donor–acceptor co-crystals are receiving increasing interest because of their many useful optoelectronic properties. While the steady-state properties of many different co-crystals have been characterized, very few studies have addressed how crystal morphology affects the dynamics of charge transfer (CT) exciton formation, migration, and decay, which are often critical to their performance in device structures. Here we show that co-crystallization of a pyrene (Pyr) electron donor with either N , N ′-bis(2,6-diisopropylphenyl)- or N , N ′-bis(3′-pentyl)-perylene-3,4:9,10-bis(dicarboximide) (diisoPDI or C 5 PDI) electron acceptors, respectively, yields mixed π-stacked Pyr–diisoPDI or Pyr–C 5 PDI donor–acceptor co-crystals. Femtosecond transient absorption microscopy is used to determine the CT exciton dynamics in these single crystals. Fitting the data to a one-dimensional charge transfer CT exciton diffusion model reveals a diffusion constant that is two orders of magnitude higher in the Pyr–diisoPDI co-crystal compared to the Pyr–C 5 PDI co-crystal. By correlating the co-crystal structures to their distinct excited-state dynamics, the effects of each mixed stacked structure on the exciton dynamics and the mechanisms of CT exciton diffusion are elucidated.more » « less
-
null (Ed.)Density functional theory (DFT) calculations were used to examine the binding strength of one and two methane molecule(s) with graphene (62 and 186 carbon atoms) and model systems of aromatic hydrocarbons (benzene, pyrene, and coronene). We explored different possibilities of binding modes of methane such as one, two, and three C-H interacting with small π-systems. Two methane molecules were considered to bind from the same as well as opposite sides of the plane of benzene and other πsystems including graphene models. Our results show that methane molecule prefers to bind with three C-H…π interactions with all the π-systems except benzene. The preference of tripod configuration of methane on the surface of graphene systems strongly agrees with the neutron diffraction experiment of methane on graphitized carbon black. The binding strength is almost doubled by increasing the number of methane molecules from one to two. Importantly, two methane molecules prefer to bind on the same side rather than opposite sides of the plane of graphene due to stabilizing CH…HC interactions between them in addition to six CH…π interactions. Interestingly, binding strength contributions from CH…HC interactions (approx. 0.4–0.5 kcal/mol) of two methane molecules on the surface are analogous to methane dimer complex free from the surface of graphene. C-H stretching frequency shifts, bond lengths, and binding distances support the presence of CH…HC interactions between two methane molecules. Structures of complexes, binding energies, and C-H stretching frequency shifts agree with available experimental datamore » « less
-
The crystal structures of two intermediates, 4-amino-3,5-difluorobenzonitrile, C7H4F2N2(I), and ethyl 4-amino-3,5-difluorobenzoate, C9H9F2NO2(II), along with a visible-light-responsive azobenzene derivative, diethyl 4,4′-(diazene-1,2-diyl)bis(3,5-difluorobenzoate), C18H14F4N2O4(III), obtained by four-step synthetic procedure, were studied using single-crystal X-ray diffraction. The molecules ofIandIIdemonstrate the quinoid character of phenyl rings accompanied by the distortion of bond angles related to the presence of fluorine substituents in the 3 and 5 (ortho) positions. In the crystals ofIandII, the molecules are connected by N—H...N, N—H...F and N—H...O hydrogen bonds, C—H...F short contacts, and π-stacking interactions. In crystal ofIII, only stacking interactions between the molecules are found.more » « less
